Castle Biosciences, Inc. ownership disclosure: RTW Investments, LP and Roderick Wong report beneficial ownership of 2,758,335 shares, representing 9.3% of Castle Biosciences' Common Stock based on February 19, 2026 outstanding share count of 29,731,198 shares.
The filing is an amendment to a Schedule 13G and states the reported shares are directly held by RTW Funds and that the RTW Funds have the right to receive dividends or sale proceeds. Shared voting and dispositive power are reported; sole voting and dispositive power are reported as zero.
Positive
None.
Negative
None.
Insights
Large passive stake reported by RTW Funds and affiliated adviser.
RTW Investments and Roderick Wong report 2,758,335 shares beneficially owned, equal to 9.3% of the outstanding Common Stock as of February 19, 2026. The stake is held by the RTW Funds; voting and dispositive power are reported as shared.
Cash‑flow treatment is stated: the RTW Funds have the right to receive dividends or proceeds from sales. Timing and any intended disposition are not disclosed in this excerpt; subsequent filings would show changes in position.
Key Figures
Shares beneficially owned:2,758,335 sharesPercent of class:9.3%Shares outstanding (reference):29,731,198 shares
3 metrics
Shares beneficially owned2,758,335 sharesreported by RTW Investments and Roderick Wong
Percent of class9.3%based on 29,731,198 shares outstanding as of Feb 19, 2026
Shares outstanding (reference)29,731,198 sharesas of <date>February 19, 2026</date> per company 10-K
"Amount beneficially owned: The information required by Item 4(a) is set forth in Rows 5 - 9"
Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.
shared dispositive powerregulatory
"Shared Dispositive Power 2,758,335.00"
Schedule 13G/Aregulatory
"Amendment No. 1 ... SCHEDULE 13G/A"
A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
(Amendment No. 1)
Castle Biosciences, Inc.
(Name of Issuer)
Common Stock, $0.001 par value
(Title of Class of Securities)
14843C105
(CUSIP Number)
03/31/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
14843C105
1
Names of Reporting Persons
RTW Investments, LP
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
2,758,335.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
2,758,335.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
2,758,335.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
9.3 %
12
Type of Reporting Person (See Instructions)
IA, PN
SCHEDULE 13G
CUSIP Number(s):
14843C105
1
Names of Reporting Persons
Roderick Wong
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
2,758,335.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
2,758,335.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
2,758,335.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
9.3 %
12
Type of Reporting Person (See Instructions)
HC, IN
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
Castle Biosciences, Inc.
(b)
Address of issuer's principal executive offices:
1500 W. Parkwood Ave., Suite 400, Friendswood, TX, 77546.
Item 2.
(a)
Name of person filing:
This statement is filed by:
(i) RTW Investments, LP ("RTW Investments"), a Delaware limited partnership and the investment adviser to certain funds (the "RTW Funds"), with respect to shares of Common Stock, par value $0.001 per share (the "Shares") of Castle Biosciences, Inc. (the "Company") directly held by the RTW Funds; and
(ii) Roderick Wong, M.D. ("Dr. Wong"), the Managing Partner and Chief Investment Officer of RTW Investments, with respect to the Shares directly held by the RTW Funds.
The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons."
The filing of this statement should not be construed as an admission that any of the foregoing persons or any Reporting Person is, for the purposes of Section 13 of the Securities Exchange Act of 1934, as amended, the beneficial owner of the Shares reported herein.
(b)
Address or principal business office or, if none, residence:
The address of the business office of each of the Reporting Persons is 40 10th Avenue, Floor 7, New York, New York 10014.
(c)
Citizenship:
RTW Investments is a Delaware limited partnership. Dr. Wong is a citizen of the United States.
(d)
Title of class of securities:
Common Stock, $0.001 par value
(e)
CUSIP No.:
14843C105
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
The information required by Item 4(a) is set forth in Rows 5 - 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The percentages set forth in Row 11 of the cover pages are calculated based upon 29,731,198 Shares outstanding as of February 19, 2026 as reported in the Company's Annual Report on Form 10-K filed with the Securities and Exchange Commission on February 26, 2026.
(b)
Percent of class:
RTW Investments: 9.3%
Dr. Wong: 9.3%
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
RTW Investments: 0
Dr. Wong: 0
(ii) Shared power to vote or to direct the vote:
RTW Investments: 2,758,335 Shares
Dr. Wong: 2,758,335 Shares
(iii) Sole power to dispose or to direct the disposition of:
RTW Investments: 0
Dr. Wong: 0
(iv) Shared power to dispose or to direct the disposition of:
RTW Investments: 2,758,335 Shares
Dr. Wong: 2,758,335 Shares
Item 5.
Ownership of 5 Percent or Less of a Class.
Not Applicable
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required.
See Item 2. The RTW Funds have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Shares reported herein.
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
Not Applicable
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
RTW Investments, LP
Signature:
/s/ Roderick Wong, M.D.
Name/Title:
Roderick Wong, M.D., Managing Partner
Date:
05/15/2026
Roderick Wong
Signature:
s/ Roderick Wong, M.D.
Name/Title:
Roderick Wong, M.D.
Date:
05/15/2026
Exhibit Information
Exhibit 99.1 Joint Filing Agreement (incorporated by reference to Exhibit 99.1 to the Reporting Persons' Schedule 13G filed with the SEC on February 17, 2026).
What stake does RTW Investments hold in Castle Biosciences (CSTL)?
RTW Investments and Roderick Wong report beneficial ownership of 2,758,335 shares, representing 9.3% of the class based on February 19, 2026 and a stated outstanding share count of 29,731,198.
Who actually holds the reported Castle Biosciences shares?
The shares are directly held by the RTW Funds, with the filing made by RTW Investments, LP as investment adviser and by Roderick Wong as Managing Partner and CIO of RTW Investments.
Does the filing show who controls voting or sale decisions for the shares?
The filing states shared voting power and shared dispositive power for 2,758,335 shares; sole voting and sole dispositive power are reported as 0 for both Reporting Persons.
Is the reported ownership percentage calculated from a specific date?
Yes. The 9.3% figure is calculated using an outstanding share count of 29,731,198 shares as of February 19, 2026, per the company’s Annual Report on Form 10-K referenced in the filing.
